1. Field of the Invention
The present invention relates to solid oxide fuel cells.
2. Related Art Statement
Recently, fuel cells have been recognized as power generating equipment. Since the fuel cell is a device capable of directly converting chemical energy possessed by fuel to electrical energy, and the fuel cell is free from any limitation of Carnot's cycle, the cell is a very promising technique owing to its high energy conversion efficiency, wide latitude of fuels to be used (naphtha, natural gas, methanol, coal reformed gas, heavy oil and the like), less public nuisance, and high electric power generating efficiency without being affected by scale of installations.
Particularly, as the solid oxide fuel cell (referred to as "SOFC" hereinafter) operates at high temperatures of 1,000.degree. C. or more, reaction on electrodes is extremely high. Thus, catalyst of a noble metal such as expensive platinum is necessary. In addition, since the SOFC has low polarization and relatively high output voltage, its energy conversion efficiency is conspicuously higher than that in other fuel cells. Furthermore, since their constituent materials are all solid, the SOFC is stable and has long use life.
In general, the SOFC is composed of an air electrode, a solid electrolyte and a fuel electrode.
FIG. 5 is a partial front elevational view illustrating one example of such a solid oxide fuel cell. This SOFC is of a monolithic design referred to as "Co-flow model" of Argonne type first proposed by Argonne National Laboratory.
As shown in FIG. 5, with the SOFC of this type, a flat plate-like air electrode film 1, an interconnector 2 and a flat plate-like fuel electrode film 3 are arranged in this order from above to below to form a flat plate-like laminate 50. Such flat plate-like laminates 50 are then arranged in parallel with one another with a predetermined interval. A number of fuel electrode films 4, which have a substantially V-shaped section as shown in the drawing, are arranged in opposition to the flat plate-like fuel electrodes 3 to form a number of fuel gas flow passages 7 in a direction orthogonal to the paper as viewed in the drawing. Moreover, a number of air electrode films 6, which have an inverted V-shaped section, are provided in opposition to the flat plate-like air electrode films 1 to form a number of oxidizing gas flow passages 8 in a direction orthogonal to the paper. These fuel gas flow passages 7 and the oxidizing gas flow passages 8 are combined with one another in the form of a mosaic, and a wavy solid electrolyte film 5 is formed between the fuel electrode films 4 and the air electrode films 6. Between the adjacent fuel gas flow passages 7 and oxidizing gas flow passages 8 are interposed the fuel electrode film 4, the wavy solid electrolyte film 5 and the air electrode film 6 in this order. The power generation is performed among these films. Although the films are shown only in one row for the sake of simplicity in FIG. 5, a number of the laminates shown in FIG. 5 are piled one upon another to form a number of gas flow passages in the form of a honeycomb.
FIG. 6 illustrates a SOFC of the Argonne type which is similar to that of FIG. 5, but referred to as "Cross flow model".
This SOFC is composed of flat plate-like laminates 50 and 51 alternately laminated. The former laminate 50 is similar to that shown in FIG. 5, and the laminate 51 is formed by arranging successively a flat plate-like fuel electrode film 3, a flat plate-like solid electrolyte film 15 and a flat plate-like air electrode film 1 arranged in parallel with one another with a predetermined interval. In each space between the two flat plate-like fuel electrode films 3 is arranged a wavy fuel electrode film 14 to form fuel gas flow passages 17 into which a fuel gas is supplied as shown by arrows A. On the other hand, in each space between the two flat plate-like air electrode films 1 is arranged a wavy air electrode film 16 to form oxidizing gas flow passages 18 into which an oxidizing gas is supplied as shown by arrows B. The fuel gas flow passage 17 and the oxidizing gas flow passage 18 are crossed by a predetermined angle, for example, 90.degree.. Between the fuel gas flow passages 17 and the oxidizing gas flow passages 18 there are interposed a flat plate-like fuel electrode film 3, a flat plate-like solid electrolyte film 15 and a flat plate-like air electrode film 1 in this order. The power generation is performed in these interposed films.
Inasmuch as such a monolithic solid oxide fuel cell of the Argonne type needs no inert structural support members, it exhibits a high output density and a high energy density, and has a wide active surface area. Therefore, it is expected, as a promising technique, which can improve its electrical power generating efficiency.
With the construction having the number of oxidizing gas flow passages and the fuel gas flow passages in the form of a honeycomb, however, it is very difficult to appropriately supply the oxidizing gas and the fuel gas into the respective flow passages and to prevent any leakage and mixing of the oxidizing gas and the fuel gas. Still less, lack of suitable gas supplying means makes it difficult to put the technique to practical use.